The present invention relates to a wire cut electric discharge machine, and more particularly to an apparatus for detecting completion of automatic wire setting, which is arranged to automatically detect completion of wire setting when a wire electrode is inserted through a hole or groove formed in a workpiece and is automatically extended between wire guides disposed above and below the workpiece prior to start of machining.
A wire cut electric discharge machine has been known, which comprises upper and lower wire guides respectively arranged above and below a workpiece table for supporting a workpiece, a wire feed mechanism for feeding the wire electrode downward while clamping it, and a wire recovery device arranged below the lower wire guide. In this conventional electric discharge machine, during electric discharge machining, the wire electrode is continuously fed downward by the wire feed mechanism, and is guided to the wire recovery device via wire paths formed in the upper and lower wire guides. In case that the wire electrode is broken and must be extended again, the wire feed mechanism is operated to draw the wire electrode downward, so that the wire electrode is inserted through the wire path of the upper wire guide, a hole or groove formed in the workpiece and the wire path of the lower wire guide, and then automatic setting of the wire electrode is performed so that the electrode extends between the upper and lower wire guides.
To detect the completion of automatic wire setting, conventionally, a limit switch, for instance, has been employed, which is disposed in a manner facing a wire feed path at a location downstream of the wire recovery device and capable of advancing to and retracting from the wire feed path. The limit switch is moved forward when the automatic wire setting is performed, so as to detect that the wire electrode has reached a specific position or the automamtic depresses an operating piece member of the limit switch.
However, the conventional apparatus for detecting the completion of automatic wire setting is complicated in construction for the reason that it includes a large number of mechanical components and requires the limit switch which is arranged for reciprocal motion, etc. Furthermore, there occurs a problem associated with an installation space of the limit switch. In particular, if the wire recovery device is of a belt drive type which is arranged to clamp the wire electrode between belts for delivery of the wire electrode, it is impossible to dispose the limit switch in a manner facing the wire recovery device, and it is very difficult to take up the installation space for the limit switch at a location downstream of the wire recovery device since an envelope member for guiding the wire electrode is dispose at an exit side of the wire recovery device.